516 THE CHICAGO ACADEMY OF SCIENCES. 
PLATE Xi 
Figure A. Genitalia of Planorbis trivolvis Say. 1, penis; 2, penis appendage; 
3, vas deferens; 4, duct (portion of vas deferens) from penis 
appendage; 5, nerve to penis appendage; 6, protractor muscles 
of penis; 7, retractor muscles of penis; 8, left retractor of buc- 
cal sac; 9, duct from prostate; 10, duct of receptaculum seminis ; 
11, receptaculum seminis; 12, oviduct; 13, prostate; 14, ovisperm 
duct; 15, ovotestis (the albuminiparous gland is omitted from 
this figure). 
B. Radula of Planorbis trivolvis Say. 1, central tooth; 2, lateral tooth; 
3, marginal tooth. 
C. Genitalia of Galba danielsi (BAKER). (Animal killed in Septem- 
ber.) 
D. Genitalia: of Galba caperata (Say). 
PLATE XIV. 
Variation in retractor and protractor muscles of male organ in Lymnea. 
Figure A. Lymnea stagnalis appressa Say. M, transverse muscles. 
B. Lymnea stagnalis sanctemarie WALKER. From Siskowit Bay, Isle 
Royale. 
C. Pseudosuccinea columella (Say). 1-3, from Sea Breeze, near 
Rochester, N. Y.; 4, from: La Porte, Ind. 
D. Bulminea megasoma (Say). 1, one penis-sac retractor; 2, two re- 
tractors of penis-sac; pr, penis retractor; psr, penis-sac re- 
tractor; ps, penis-sac; psp, posterior penis-sac protractors; psp’, 
anterior penis-sac protractors. 
E. Galba parva (LEA). 
F. Galba umbilicata (ApAMS). Cayuga Lake, N. Y. 
G. Galba obrussa (Say). 1, Sea Breeze, N. Y.; 2, Cayuga Lake, N. Y. 
G, 3. Galba obrussa peninsulae (WALKER). 
PEATE XY. 
Variation in muscles of male organ. 
Figure A. Galba reflera (Say). La Porte, Indiana. 
B. Galba emarginata (Say). From Isle Royale specimens. 
C. Galba palustris (MU.iEr). Colorado specimens. ap, anterior penis- 
sac protractors; cm, columellar muscle; pp, posterior penis-sac 
protractors; pr, penis retractor; psr, penis-sac retractor. 
D. Galba reflexa (Say). Calumet Lake, Illinois. 
E. Acella haldemani ((DeEsH.) BINNEY.) 
F. Galba catascopium adamsi BAKER. 1-3, St. Clair flats, Mich. 
F. Galba catascopium (Say). . 4-6, Erie Canal, Rochester, N. Y.; 7-8, 
Genesee River, Rochester, N. Y. 
G. Galba elodes jolietensis (BAKER). 
PLATE-XYI. 
FOSSIL LYMNAS. 
Figure 1. Lymnea ativuncula Wuite. Bull. U. S. Geol. Surv., No. 29, pl. 4, 
fig. 10. Type. 
